Nest predation versus resources in a Neotropical passerine: constraints of the food limitation hypothesis

Abstract

Food limitation is one explanation for differences in life-history traits, such as clutch size or nestling mortality, between tropical and temperate birds. Also predation has been con-sidered one of the major factors shaping life-histories. We found mixed support for the food-limitation hypothesis when we experimentally manipulated food abundance and evaluated subsequent effects on breeding and behavioural parameters of the Blue-black Grassquit (Volatinia jacarina). Food-provisioned males increased territorial disputes and received more female visits, and a higher proportion of supplemented pairs produced more eggs and had faster growth rates in their broods compared to non-provisioned pairs. However, egg laying was delayed in the fed group. Unexpectedly, predation in the food-provisioned group was twice that of the control group. We presume that nest detection by predators increased due to higher nest attentiveness in food-provisioned nests. Food availability constitutes a proximate mechanism resulting in changes in behaviours and breeding parameters, but nest predation may be the prevailing selective pressure.